People exposed to loud industrial, military or other noise need to be protected by suitable Hearing Protection Devices. The best solution is to use individually fit earplugs. However, it is difficult to know the real (in site) performance of such devices, as it depends on the morphology of the user's ear canal as well as on the way it is put in place by the user. Different types of earplugs (foam, pre-molded and moldable) are available in different sizes. All these parameters make it difficult for the user to choose a well-adapted earplug for his ear. It is therefore important to find a robust, fast, and easy method helping the user to choose correctly the earplug adapted to the morphology of his ear. The proposed method uses a prototype of an instrumented earplug (loudspeaker and microphone) allowing different types of tips to be fixed. As in the range of very low-frequency (below 90 Hz) the frequency response of the loudspeaker depends strongly on the proper sealing (airtightness) of the earplug in the ear canal, and therefore it may be used as a measurement for the earplug's fitting. If there is a leak, the frequency response will drop in the low-frequency domain. The method using these properties has been implemented in a DSP coupled with the instrumented earplug. A single measurements takes less than one minute and the developed prototype indicates the result with a color code: Red LED - leak; Green LED - airtight. REAT (Real-Ear Attenuation at Threshold) measurements using 3 sizes of existing earplugs have been realized and show a strong correlation between the airtightness (no acoustic leak) measured by the system and the performance of the earplug.
